Interpretive Summary: Tick- and mosquito-borne diseases pose serious threats to humans throughout much of the habitable world. Repellents provide a critical means of personal protection against ticks and mosquitoes and effective insecticides suppress mosquito populations. Trees and shrubs in the cypress family appear to be a rich source of bioactive chemicals. We evaluated the essential oils from three species of trees in the cypress family for repellent activity against ticks and repellent and insecticidal activity against mosquitoes. One essential oil repelled mosquitoes and two oils repelled ticks with an effectiveness similar to that of the widely used synthetic repellent deet. The oils killed few mosquito larvae and were not toxic to adult mosquitoes. These findings are of interest to researchers involved in repellent discovery and development. At least one oil, may deserve the attention of manufacturers that produce repellents based on naturally occurring chemicals.

Technical Abstract:
Juniperus communis leaf oil, J. chinensis wood oil and Cupressus funebris wood oil (Cupressaceae) from China were analyzed by gas chromatography and gas chromatography-mass spectrometry. We identified 104 compounds representing 66.8-95.5% of the oils. The major components of J. communis were a-pinene (27.0%), a-terpinene (14.0%) and linalool (10.9%), of J. chinensis were cuparene (11.3%) and d-cadinene (7.8%), and of C. funebris were a-cedrene (16.9%), cedrol (7.6%) and ß-cedrene (5.7%). The three essential oils were evaluated for repellency against host-seeking nymphs of the lone star tick, Amblyomma americanum (L.) and the blacklegged tick, Ixodes scapularis Say, in laboratory bioassays. All the oils were repellent to both species of ticks. The EC95 values of C. funebris and J. communis against A. americanum were 426, 508, and 917 µg oil/cm2 filter paper, respectively, compared to 683 µg oil/cm2 filter paper of deet (N,N-diethyl-3-methyl benzamide). All I. scapularis nymphs were repelled by 103 µg oil/cm2 filter paper of C. funebris oil. At 4h after application, 823 µg oil/cm2 filter paper, C. funebris and J. chinensis oils repelled =80% of A. americanum nymphs. The oils of C. funebris and J. chinensis did not prevent female Aedes aegypti from biting at the highest dosage tested (1.500 mg/cm2). However, the oil of J. communis had a Minimum Effective Dosage (estimate of ED99) for repellency of 0.029 ± 0.018 mg/cm2; this oil was nearly as potent as deet (MED of 0.008 ± 0.004 mg/cm2 ). The oil of J. chinensis showed mild ability to kill Ae. aegypti larvae, at 80 and 100% at 125 and 250ppm, respectively.